diag: Add protection while de-initializing clients

Currently, while de-initializing clients, there is
a possibility of using already freed memory. The
patch adds proper protection to fix the issue.

CRs-Fixed: 2068569
Change-Id: I4b397a82e03fa2f1c84cfa8ca912cdb6a51ba08b
Signed-off-by: Mohit Aggarwal <maggarwa@codeaurora.org>